The invention relates to reflectance sensors built up from an optical unit, a sample analysis unit and a system control unit, and to a method of measuring the reflectance of a sample in the form of a liquid pigment preparation, and to the use of a reflectance sensor according to the invention for the measurement of the reflectance of liquid pigment preparations in various process stages during the production, further processing and use of the liquid pigment preparations.
During the production of liquid pigment preparations such as paint or enamel mixtures, pigment pastes, white let-downs or other color mixtures, a reproducible color and hiding power of the mixtures is important. This reproducibility is ensured by regular product control during the production of the liquid pigment preparations, either visually or with the aid of spectroscopic methods. According to the prior art, control is carried out by mixing the desired color mixtures, applying to a substrate and drying, curing or stoving and subsequent analysis of the colored layers obtained. Although this method is accurate, it is very time-consuming.
A significant saving in time can be achieved by the measurement being carried out directly on the liquid pigment preparations, so that application of colored layers to the substrate and subsequent drying of the layers is not required.
In principle, all commercial color measuring instruments are suitable for this task. Each VIS sensor which operates in reflectance is likewise suitable for this.
For example, EP-A 0 472 899 relates to a photometric measuring device for measuring the level of attenuation during the propagation of light in disperse systems. This device is built up from a through-flow cuvette for the sample to be examined, with at least one lateral opening for the optical connection of at least one optical waveguide. From a light source, an optical waveguide connection leads to the interior of the cuvette with the sample to be examined and from there to an optical detector to generate a measured signal. A direct optical waveguide connection leads directly from the light source to the optical detector to generate a reference signal. Furthermore, the photometric device comprises an evaluation device connected to the optical detector.
WO 98/16822 relates to an analysis system for the analysis of the physical properties of coatings, pigment pastes or similar systems, which is built up from an apparatus for forming a film of the coatings, pigment pastes and similar systems with a specific thickness, a light source for irradiating the coating to be examined or pigment paste or similar systems to be examined, interaction occurring between the light and the coating, the pigment paste or similar system, a measured signal being generated; and from an apparatus for recording the measured signal and from a detector connected to the apparatus for picking up the measured signal.
Disadvantageous with these systems is the inadequate measurement accuracy which can be achieved with the measuring arrangements known from the prior art.